DE102017205695A1 - Method for determining an armature stroke of a fuel injector - Google Patents

Abstract

The invention relates to a method for determining an armature stroke (A-A) of a fuel injector with a piezoelectric needle-closing sensor. During opening of a switching valve of the fuel injector, a total signal drop (G) of the needle closing sensor and a signal dip (S) within the total signal drop (G) are detected. The armature stroke (A-A) is determined from a ratio between the total signal drop (G) and the signal dip (S).

Description

The present invention relates to a method for determining an armature stroke of a fuel injector with a piezoelectric needle closing sensor. Furthermore, the present invention relates to a computer program which is set up to carry out each step of the method according to the invention and to a machine-readable storage medium on which the computer program according to the invention is stored. Finally, the invention relates to an electronic control unit which is set up to determine an armature stroke of a fuel injector with a piezoelectric needle-closing sensor by means of the method.

State of the art

The armature stroke of a fuel injector for the common rail injection of fuel can be set to 1 micron accurate. Due to wear, runtime effects and various operating conditions, the actually present or achieved anchor stroke can scatter much more. In particular, too small anchor strokes are problematic for the injector function because they can lead to seat throttling and thus significantly reduced injection quantity. Too high anchor stroke is problematic with respect to wear.

The evaluation of the signal of a piezoelectric needle closing sensor (NCS) allows a conclusion on the armature stroke. The use of such a piezoelectric needle closing sensor is in DE 10 2014 204 098 A1 described. Due to the not exactly known piezoelectric properties of the needle-closing sensor, however, this method is inaccurate. Thus, during operation and over the life of the needle-closing sensor, a scattering of its piezoelectric longitudinal effect (d33 effect) of up to 30% takes place. This describes the ratio of the force acting on the piezoelectric element of the needle closing sensor mechanical force and the parallel generated electric field, which generates the sensor signal.

Disclosure of the invention

In the method for determining an armature stroke of a fuel injector with a piezoelectric needle-closing sensor, a total signal drop of the needle closing sensor and a signal drop within the total signal drop are determined during opening of a switching valve of the fuel injector. The armature stroke is determined from a ratio between the total signal drop and the signal dip. In particular, the fuel injector is a common rail fuel injector for direct fuel injection.

The method allows the determination of the armature stroke even if the piezoelectric longitudinal effect of the needle closing sensor is not known. This can be determined in a factory in the measurement of hydraulic test points of the fuel injector on the one hand, the distance to the seat throttle limit and, secondly, also fuel injectors can be identified with too large anchor stroke. In addition, the method allows to monitor the armature drift behavior during operation in order to then counteract accordingly if necessary.

Due to hydraulic effects, during the upward movement of the armature during switching valve opening shortly before reaching the stroke stop, the armature movement stops. In the signal of the needle closing sensor, this pause of the armature movement, in particular in the case of small armature strokes, becomes noticeable as a signal collapse. The severity of the signal dip depends on the armature stroke. With decreasing armature stroke the expression increases, with larger anchor strokes no signal collapse is recognizable. In this case, the armature stroke can be in particular in the range of 10 microns to 30 microns. The quantitative signal collapse depends not only on the armature stroke but also on the piezoelectric longitudinal effect of the needle-closing sensor and can therefore not be used directly for determining the armature stroke. However, if one compares the signal drop with the total signal drop during the opening process (this is proportional to the armature stroke), the resulting ratio depends solely on the armature stroke and no longer on the piezoelectric longitudinal effect of the needle closing sensor.

The total signal drop can be determined, in particular, as the difference between an electrical signal of the needle-closing sensor when the switching valve is closed and a local minimum of the electrical signal of the needle-closing sensor when the switching valve is open. The electrical signal of the needle closing sensor with closed switching valve is ideally zero. By relaxing the piezoelectric element of the needle closing sensor when opening the switching valve, a negative electrical signal is generated.

The signal collapse is determined in particular as the difference between the local minimum of the electrical signal of the needle-closing sensor when the switching valve is open and a local maximum of the electrical signal of the needle-closing sensor when the switching valve is open.

The electrical signal may be a voltage applied to the piezoelectric element. If the piezoelectric element is connected via a low-resistance resistor, the current delivered by the piezoelectric element can be used as the electrical signal instead of the voltage.

Determining the anchor stroke is preferably carried out by means of a characteristic which describes the dependence of the ratio of the armature stroke. Such a characteristic curve can be easily generated from theoretical considerations or from empirical measurements.

After the armature stroke has been determined, it is preferable to determine the piezoelectric longitudinal effect of the needle closing sensor from the armature stroke.

This value may then be used to increase the accuracy with which an operating event of the fuel injector may be detected from a signal of the needle-closing sensor. Such operating events are, for example, a start of opening of the switching valve, a force increase at the start of the opening of the switching valve, an end of the opening of the switching valve, a pressure loss in a valve chamber of the fuel injector with the switching valve open, cavitation noise with the switching valve open, a start of closing the switching valve , an end of the closing of the switching valve, a needle reversal of a needle valve of the fuel injector, a pressure overshoot in the valve space at the needle reversal, a valve bouncing of the needle valve, a change in the pressure in the valve chamber during closing of the needle valve needle, a change in the pressure in the valve space between the States open and closed switching valve with open needle valve needle and needle closing the needle valve.

In one embodiment of the method, the piezoelectric longitudinal effect is determined by evaluating a dependence of the total signal drop on the armature stroke and on the longitudinal piezoelectric effect. An amount of the quotient of the total signal drop and the piezoelectric longitudinal effect increases with increasing armature stroke. If the armature stroke is known, then the piezoelectric longitudinal effect can be determined. For this purpose, the dependency can in particular be stored as a characteristic curve created from theoretical considerations or from empirical measurements.

In another embodiment of the method, the determination of the piezoelectric longitudinal effect takes place by evaluating a dependence of the signal dip on the armature stroke and on the piezoelectric longitudinal effect. An amount of the quotient of the signal collapse and the piezoelectric longitudinal effect decreases with increasing armature stroke. If the armature stroke is known, then the piezoelectric longitudinal effect can be determined. For this purpose, the dependency can in particular be stored as a characteristic curve created from theoretical considerations or from empirical measurements.

The computer program is set up to perform each step of the method, in particular when it is performed on an electronic computing device or controller. For this purpose it is stored on the machine-readable storage medium. The computer program allows the simple implementation of the method in an existing control unit, without having to make structural changes. By loading the computer program on a conventional electronic control unit, the electronic control unit is obtained, which is adapted to determine an armature stroke of a fuel injector with a piezoelectric needle closing sensor.

list of figures

• 1 ist eine Querschnittsdarstellung eines Kraftstoffinjektors, dessen Ankerhub mittels eines Verfahrens gemäß einem Ausführungsbeispiel der Erfindung ermittelt werden kann.
• 2 zeigt einen Detailausschnitt aus dem Kraftstoffinjektors gemäß 1.
• 3 zeigt in einem Diagramm die zeitlichen Verläufe von Spannungssignalen eines Nadelschließsensors des Kraftstoffinjektors gemäß Fig. 1 für unterschiedliche Ankerhübe.
• 4 zeigt in einem Diagramm die Abhängigkeit eines Gesamtsignalabfalls und eines Signaleinbruch vom Ankerhub in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens.
• 5 zeigt in einem Diagramm die Abhängigkeit eines Verhältnisses des Gesamtsignalabfalls und des Signaleinbruch vom Ankerhub in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens.

An embodiment of the invention is illustrated in the drawings and explained in more detail in the following description.

• 1 is a cross-sectional view of a fuel injector whose armature stroke can be determined by a method according to an embodiment of the invention.
• 2 shows a detail of the fuel injector according to 1 ,
• 3 shows a diagram of the time courses of voltage signals of a needle closing sensor of the fuel injector of FIG. 1 for different armature strokes.
• 4 shows in a diagram the dependence of a total signal drop and a signal drop from the armature stroke in one embodiment of the method according to the invention.
• 5 shows in a diagram the dependence of a ratio of the total signal drop and the signal drop from the armature stroke in one embodiment of the method according to the invention.

Embodiment of the invention

An embodiment of the invention is based on a fuel injector 10 described from the DE 10 2009 029 549 A1 is known and in 1 is shown. This fuel injector 10 includes an injector body 11 in which a valve piston 12 is arranged. This is at an upper end in a valve piece 13 guided. Its lower end extends in the direction of a nozzle 14. The valve piston 12 is with the valve needle 15 a needle valve 16 connected inside the nozzle 14 is arranged. In addition, the valve piston 12 is provided with a high pressure bore 17 and with a return bore 18 connected. At an upper end of the fuel injector 10 are a magnetic head 19, an anchor group 20 and a return 21 arranged. The fuel injector 10 is further connected via an electrical connection 22 with an electrical power source (not shown) and via a high pressure port 23 comprising a rod filter connected to a fuel supply line (not shown).

When operating the fuel injector 10 is provided that the magnetic head 19 is energized, causing the anchor group 20 is moved towards the magnetic head. This opens the connection between a control room 24 above the valve piston 12 and the return 21 , This triggers a drop in the pressure in the control chamber 24 and thus an opening movement of the composite of valve piston 12 and valve needle 15 out. By opening the needle valve 16 becomes the connection between the high pressure bore 17 and the spray holes of the nozzle 14 manufactured, whereby fuel to the nozzle 14 conveyed and injected into a cylinder of an internal combustion engine.

According to 2 is inside the injector body 11 a high pressure room 25 as well as a low-pressure room 26 arranged. These two spaces are separated from each other by the valve piece 13 separated. The high pressure room 25 communicates with the high pressure port 23. The low pressure space 26 is about the return 21 connected to a fuel tank. The high pressure room 25 is with the nozzle 14 connected. The nozzle-distal end of the valve piston 12 is displacer effective in the valve piece 13 arranged control room 24 arranged. The control chamber 24 communicates via an inlet throttle 27 with the high pressure chamber 25 and a throttled drain channel 28 with the low pressure space 26, wherein the drainage channel 28 by means of a switching valve 29 is controlled. When the drainage channel 28 by means of the switching valve 29 is shut off and the valve needle 15 is in its closed position, is in the control chamber 24, the same high pressure as in the high-pressure chamber 25 a, with the result that the valve piston 12 pressed downwards and the associated valve needle 15 in the the needle valve 16 shut off closing position is held. Becomes the drainage channel 28 by means of the switching valve 29 opened, turns in the control room 24 one opposite the high pressure in the high pressure chamber 25 reduced pressure on, and the valve piston 12 shifts together with the valve needle 15 in the upward direction, that is the valve needle 15 is placed in its open position, allowing fuel through the nozzle 14 is injected into the combustion chamber.

The switching valve 29 has a sleeve-shaped closing body 30 , which is formed by a closing spring 34, which is designed as a helical compression spring, against a to the outlet port of the drain channel 28 concentric seat is tensioned. In the example of 2 the seat is designed as a plane surface on which the sleeve-shaped closing body 30 is seated with a line-shaped annular edge. The sleeve-shaped closing body 30 is on a to the longitudinal axis L of the injector body 11 coaxial guide rod 31 guided axially displaceable, wherein the annular gap between the inner periphery of the closing body 30 and the outer periphery of the guide rod 31 is designed as a practically leak-free throttle or sealing gap. When the closing body 30 in the 2 shown closed position assumes that within the closing body 30 formed valve chamber 32, which via the drainage channel 28 with the control room 24 communicates and then correspondingly has the same fluid pressure as the control chamber 24, compared to the low pressure space 26 shut off.

During the closed phase of the valve piston 12 connected valve needle 15, that is, when the needle valve is closed 16 , is the switching valve 29 closed, and in the valve room 32 as well as in the control room 24 the same fluid pressures are present. Immediately before the closing time of the valve needle 15 the pressure in the control room drops 24 because of the low pressure at that time under the nozzle seat of the valve needle 15 and the associated closing movement of the valve piston 12 under the high pressure in the high pressure port 23 from. Immediately after closing the valve needle 15 it comes because of the now stationary valve piston 12 to a steep rise in pressure in the control room 24 , where the control chamber pressure on the pressure in the high pressure port 23 increases. The pressure in the control room 24 and the virtually identical pressure in the valve chamber 32 thus indicate the closing time of the valve needle 15 a pronounced minimum.

Because the pressure of the control room 24 with closed closing body 30 is also present in the valve chamber 32, the guide rod 31 inside the closing body 30 in this valve position the front side always loaded by the control chamber pressure. The valve chamber pressure is by means of the guide rod 31 on a small piezo element as a needle closing sensor 33 derived. Electrical connections of the needle closing sensor 33 are connected to externally accessible plug contacts, so that one of the needle closing sensor 33 provided voltage can be read out as an electrical signal U. This is less an offset voltage proportional to the pressure in the valve chamber 32 , The read electrical Signal U is passed to a controller (not shown), which controls the fuel injector 10 controls.

In 3 is the time course of the electrical signal U when opening and re-closing the switching valve 29 for different anchor strokes A ₁ to A _{5 of} the anchor group 20 shown, with A ₁ corresponds to the lowest armature stroke and A ₅ corresponds to the highest armature stroke. Starting from a signal of 0 V with closed switching valve 29 falls the electrical signal U in each case to a local minimum. This waste is referred to as the total signal drop G. When the switching valve 29 is closed, the electrical signal U rises again to its initial value. In the electrical signal U is a pause of the armature movement as signal collapse S can be seen. As the armature stroke decreases, the severity of the signal dip S increases.

4 shows how the total signal drop G, which corresponds to the quotient of the theoretical total signal drop Gt by the piezoelectric longitudinal effect d ₃₃ , and the signal drop S, which corresponds to the quotient of the theoretical signal drop St by the piezoelectric longitudinal effect d ₃₃ , in each case depends on the armature stroke A. As a theoretical total signal waste Gt and theoretical slump signal St which is independent of the piezoelectric longitudinal effect ₃₃ d values of the total decrease in signal G and the signal S slump are hereby referred to. The ratio V of the theoretical total signal drop S _g and the theoretical signal drop S _s is given by Formula 1: $$V=\frac{S}{G}=\frac{\raisebox{1ex}{$S_t$}\!\left/ \!\raisebox{-1ex}{$d_{33}$}\right.}{\raisebox{1ex}{${\mathrm{<figure-callout\; id="33"\; label="G\; t\; d"\; filenames="DE102017205695A1\_0002.png"\; state="\{\{state\}\}">G\; </figure-callout>}}_t$}\!\left/ \!\raisebox{-1ex}{$d_{}$}\right.}=\frac{S_t}{G_t}$$

Thus the ratio V is not dependent on the piezoelectric longitudinal effect d _33rd It is in 5 represented as a function of armature stroke A. This dependence between the armature stroke A and the ratio V is stored as a characteristic in the control unit. After calculating the ratio V, therefore, the armature stroke A can be determined.

Furthermore, the dependence of the total signal drop G and the signal drop S from armature stroke A are according to 4 stored in the control unit as characteristic curves. As soon as the armature stroke A has been determined, the piezoelectric longitudinal effect d ₃₃ can be determined from this and from the measured total signal drop G or the measured signal drop S.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014204098 A1 [0003]
• DE 102009029549 A1 [0017]

Claims (9)

A method for determining an armature stroke (A) of a fuel injector (10) with a piezoelectric needle closing sensor (33), wherein during opening of a switching valve (29) of the fuel injector (10) a total signal drop (G) of the needle closing sensor (33) and a signal collapse (S ) within the total signal drop (G) are determined and from a ratio (V) between the total signal drop (G) and the signal dip (S), the armature stroke (A) is determined. Method according to Claim 1 , characterized in that the total signal drop (G) as difference between an electrical signal (U) of the needle closing sensor (33) with closed switching valve (29) and a local minimum of the electrical signal (U) of the needle closing sensor (33) with open switching valve (29 ) is determined. Method according to Claim 2 , characterized in that the signal drop (S) as the difference between the local minimum of the electrical signal (U) of the needle closing sensor (33) with open switching valve (29) and a local maximum of the electrical signal (U) of the needle closing sensor (33) when open Switching valve (29) is determined. Method according to one of Claims 1 to 3 , characterized in that the determination of the armature stroke (A) takes place by means of a characteristic which describes the dependence of the ratio (V) on the armature stroke (A). Method according to one of Claims 1 to 4 , characterized in that from the armature stroke (A), a piezoelectric longitudinal effect (d ₃₃ ) of the needle closing sensor (33) is determined. Method according to Claim 5 Characterized in that the determination of the piezoelectric longitudinal effect (d ₃₃₎ is carried out by a function of the total signal drop (G) or said signal slump (S) of the armature stroke (A) and by the piezoelectric longitudinal effect (d ₃₃₎ is evaluated. Computer program, which is set up, each step of the procedure according to one of Claims 1 to 6 perform. Machine-readable storage medium on which a computer program is based Claim 7 is stored. An electronic control unit adapted to control an armature stroke (A) of a fuel injector (10) with a piezoelectric needle closing sensor (33) by a method according to any of the preceding claims Claims 1 to 6 to investigate.

Images